dup loop

/d[y]oop loop/ (also "dupe loop") [FidoNet] An
infinite stream of duplicated, near-identical messages on a
FidoNet echo, the only difference being unique or mangled
identification information applied by a faulty or incorrectly
configured system or network gateway, thus rendering dup
killers ineffective. If such a duplicate message eventually
reaches a system through which it has already passed (with the
original identification information), all systems passed on
the way back to that system are said to be involved in a dup
loop.